[clang] [llvm] [AMDGPU][clang][CodeGen][opt] Add late-resolved feature identifying predicates (PR #134016)

[John McCall via llvm-commits]

rjmccall wrote:

Recognizing when the `if` condition is just a call to the builtin (possibly parenthesized or `&&`ed) seems totally sufficient to me. You could check that the builtin isn't used in any other position if you want, but I don't think that's really necessary.

https://github.com/llvm/llvm-project/pull/134016